Chlamydia are obligate intracellular procaryotes that are structurally similar to gram-negative bacteria. There are two species, Chlamydia trachomatis and C. psittaci. C. trachomatis is a specific human pathogen, whereas C. psittaci is a pathogen of a variety of non-primate species. Diseases caused by C. trachomatis present a major health problem throughout the world. In developing countries, C. trachomatis causes hyperendemic trachoma which is the world's leading cause of preventable blindness. There are approximately two million people in the world today who are blind as a result of trachoma and an estimated 500 million more who are affected by this disease. In industralized nations, C. trachomatis is a sexually transmitted pathogen that causes an array of genital tract and associated infections whose incidence is increasing at epidemic rates. Conservative estimates indicate that in the United States alone there are 7-10 million C. trachomatis infections per year. In addition to their vertebrate hosts, chlamydial-like organisms have also been identified in tissues of spiders (Coelotus luctuosus) and clams (Mercenarie mercenaria), suggesting that chlamydiae are ubiquitous parasites present throughout the animal kingdom.
Biologically, Chlamydia are distinguished from all other intracellular procaryotes by their unique life cycle and molecular mechanisms of pathogenesis. The life cycle consists of two cell types, the elementary body and the reticulate body, which differ both morphologically and functionally. The elementary body is the extracellular cell type; it is metabolically inactive and is the infectious form of the parasite. The elementary body is unique in that it is efficiently phagocytized, even by nonprofessional phagocytes, and once internalized, it prevents phagolysosomal fusion. Mediators of these pathogenic mechanisms are believed to be surface components of the elementary body; however, their identity and biochemical nature is currently unknown.
Despite their common biology, C. trachomatis and C. psittaci share only 10% DNA homology and demonstrate little antigenic relatedness among their surface protein constituents. They do, however, share a common outer membrane qlycolipid antigen that has been shown to be a lipopolysaccharide (LPS) antigenically similar to the Re LPS chemotype isolated from mutants of Salmonella spp. (Caldwell et al: Inf. & Imm. 44 : 306-314 [1984]). Despite the similarities between chlamydial LPS and the Re LPS of enteric bacteria, chlamydial LPS contains a periodate sensitive antigenic determinant that is common to Chlamydia but is not found in a variety of enteric bacteria. This antigenic determinant has been defined by monoclonal antibody and termed the genus-specific LPS antigen (see Caldwell et al, above). The biological function of chlamydial LPS is unknown, but the conserved nature of the LSP epitope in an otherwise antigenically diverse genus suggests that this epitope may be functionally important with respect to the molecular mechanisms of pathogenesis shared by these obligate intracellular parasites.
The clone JM109(pFEN207), equivalent to ATCC Accession No. 53041, was deposited in the American Type Culture Collection on Feb. 27, 1985, in the patent deposit for a term of at least thirty years and complying with the time requirements of the Budapest Convention.